Lab Activity - Cellular Respiration in Yeast Name ...

[Pages:5]Lab Activity - Cellular Respiration in Yeast

Name ______________________

Questions to be investigated How can we determine the differences between anaerobic and aerobic respiration? How do variable sugar concentrations affect the rate of respiration?

Objectives Identify dependent and independent variables. Understand the process of cellular respiration. Understand the difference between anaerobic and aerobic respiration. Use proper laboratory techniques and follow a scientific process.

Materials in bins: Erlenmeyer flasks that hold at least 25 ml (4) Method for labeling test tubes (1) Baker's yeast (2 mL) Water balloons (4) Ruler (1) Warm sucrose solution, 1%, 5%, (~25 mL of each concentration), 10% (~125 mL)

To make sucrose solution: 1%: add 0.5 g of sugar to 49.5 mL of water 5%: add 2.5 g of sugar to 47.5 mL of water 10%: add 5 g of sugar to 45 mL of water Warm tap water is added until the final level of liquid is exactly 50 mL.

Safety Concerns Do not eat or drink from lab equipment.

Real-World Connections Bread making. The rate of carbon dioxide production through yeast fermentation.

Cellular Respiration in Yeast BACKGROUND INFORMATION:

All living cells, including the cells in your body and the cells in yeast, need energy for cellular processes such as pumping molecules into or out of the cell or synthesizing needed molecules. ATP is a special molecule which provides energy in a form that cells can use for cellular processes.

Cellular respiration is the process that cells use to transfer energy from the organic molecules in food to ATP. The following equation summarizes the chemical changes that occur in cellular respiration of the monosaccharide glucose when oxygen is available.

C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP

glucose

oxygen carbon

water

energy

gas dioxide gas

The chemical reactions in cellular respiration are similar to the chemical reactions when organic compounds are burned, but of course no ATP is produced. Instead energy is released in the form of light and heat. The following equation shows the chemical changes that occur when the monosaccharide glucose is burned.

C6H12O6 + 6 O2 6 CO2 + 6 H2O + light + heat

glucose

oxygen carbon

water

energy

energy

gas dioxide gas

What are the similarities between this equation for burning glucose and the equation for cellular respiration of glucose when oxygen is available? What is the difference between these equations? How does ATP, light and heat differ from an energy standpoint? There is another important feature of cellular respiration which is not shown in these equations. Cellular respiration involves many small steps; these multiple steps allow the cell to use the energy from each glucose molecule efficiently in order to make as many ATP molecules as possible. The multiple steps of cellular respiration are described in your textbook. Our description will focus on some major steps and how these steps differ, depending on whether oxygen is available or not. The first major step in cellular respiration is glycolysis: 1 glucose 2 pyruvate + 2 ATP What happens next depends on whether or not oxygen is available to the cells. When oxygen is available, cells can use the Krebs cycle and the electron transport chain to make up to 36 ATPs.

2 pyruvate + 6 O2 6 CO2 + 36 ATP Cellular respiration that uses O2 is called aerobic respiration. Most of the time, the cells in our bodies use aerobic respiration:

When oxygen is not available, however, cells use anaerobic processes to produce ATP. (The "an" in front of aerobic means "not aerobic".) Under anaerobic conditions, many cells use a process called fermentation to make ATP. As shown in the figure above, there are two types of fermentation: Lactic acid (or lactate) fermentation (e.g. in muscles when an animal exercises hard) and alcoholic fermentation (e.g. by yeast to make wine and beer). Fermentation has two disadvantages compared to aerobic respiration: (1) Fermentation produces much less ATP than aerobic respiration, and (2) fermentation produces a toxic byproduct (either lactate, which becomes lactic acid, or alcohol). However, fermentation is very useful if oxygen is not available. Use the above information to complete the figures below. Fill in the ovals with the appropriate molecule. On the blank lines write the name of the appropriate process. In the boxes at the bottom of the figure write how much ATP is made in each pathway.

With Oxygen (AEROBIC)

Without Oxygen (ANAEROBIC)

Humans use yeast every day. What is yeast? What are some common uses of yeast?

If you want to make your own bread, you can buy yeast in the grocery store. This yeast consists of little brown grains. The little brown grains of yeast may not seem to be alive, but if you put them in water with sugar, the yeast will carry out cellular respiration and grow.

You can grow yeast in a test tube filled with water and sealed with a balloon. Do you think these growth conditions are aerobic or anaerobic? Under anaerobic conditions, yeast carries out alcoholic fermentation, so it produces _________________ and ____________________. You can measure the rate of fermentation in yeast by measuring the amount of carbon dioxide gas the yeast produces. Carbon dioxide production can be measured by measuring the depth of the layer of bubbles trapped in foam on top of the yeast solution and also by observing the balloons, which catch the carbon dioxide produced and get bigger.

Part I - Sucrose Concentration

What is sucrose?

Your first experiment will investigate the effect of sucrose concentration on the rate of cellular respiration in yeast. Yeast can convert sucrose into glucose and use it during cellular respiration.

You will design an experiment to answer the question: Does the concentration of sucrose affect the rate of cellular respiration in yeast?

Mr. F will provide you with yeast, test tubes, balloons, rulers, and four concentrations of sucrose water: 0% (plain water), 1%, 5% and 10% sucrose.

1. Write a hypothesis that you will test to help you answer the research question.

2. What will be the independent variable in your experiment?

3. What will be the dependent variable in your experiment?

4. What will be the control treatment in your experiment?

What is the purpose of this control treatment? 5. The basic procedure to measure cellular respiration is:

1) Add 23 mL of the appropriate sucrose solution to each tube. 2) Add 2 mL of yeast to each tube (Measured in a 10mL graduated cylinder or with a 1 mL pipette). 3) Put a balloon on the top of each tube and tape around the base of the balloon to assure it's secure. 4) With your palm sealing the top, shake each tube until the yeast is dissolved. 5) Measure the depth of bubbles produced and observe how the balloons change after 10 minutes, 20 minutes, 30 minutes, and for 24 hours.

Write your specific procedures here (they should be MUCH MORE detailed than those above):

6. Complete the first column of these data tables.

Depth of CO2 bubbles in: Sucrose 10 minutes 20 minutes 30 minutes treatment

24 hours

Sucrose treatment

10 minutes

Balloon description

20 minutes

30 minutes

24 hours

7. Perform your experiment and record your data in the data tables. 8. Did the yeast produce different amounts of carbon dioxide with different sucrose concentrations?

Do the results match your hypothesis?

9. Discuss your results with your group. What conclusions concerning the relationship between sucrose concentration and the rate of cellular respiration are supported by your results? Continue on the back of this page if additional space is needed. REMEMBER: use the proper format for a conclusion to complete this final question. It should take some time and involve some data-related thought. Use the conclusion writing work we did during the unit on the scientific method to make this section perfect!!

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